Pre-Occupied
by Ersatz Writer
Summary: In which Saitama discovers that Genos is easier to please than expected.


**A/N:** Happy New Year everyone! Honestly? I literally _just_ started reading OPM yesterday, and then this happened, so I guess that's saying something. I just hope the characterisation is alright. Genos is so unbelievably adorable, where has he been all my life?

* * *

The whine is high, soft, almost inaudible, but most definitely _there_.

Mildly irritated, Saitama rolls to his side and claps a hand over his ear. The summer nights are still heated, despite the cooling breeze which whispers through the open window, and it had already been difficult enough as it is to sleep without that-

 _Bzzzzzzzzz_

He waits this time, holding his breath as he pinpoints the source of the noise and–

His hand snaps out, clamping down with such ferocity and speed that the air ripples and snaps under the brutal power of it all. Saitama waits for the rush to die down, muscles tense and alert. The silence which follows is almost deafening in its verdict, and, with painful slowness, he eases his fist, finger by finger.

Empty.

 _Bzzzzzzzzz_

The bald hero feels a sudden, inexplicable urge to scream.

 _Why?! Why?! Why?! Goddamn mosquitoes! Every. Freaking. Time!_

He sits up, breathing heavily with frustration. The mere thought of sleeping has been difficult enough as it is and now there is definitely no way that he could rest. In the dim lighting of the room, the darkness swells around him and the sound of the buzzing insect is an almost palpable being, elusive, teasing, but always _there_.

 _Bzzzzz_

 _Behind!_ He thinks, whipping around so sharply that his arm seems to _shatter_ the air itself. _No… It's gone… Above!_ He's on his feet now, palms slapping together with such force that he is sure he hears something vital in the building's infrastructure give.

 _Bzz_. Inexplicably now, there is a pause. Saitama would like to believe that he's finally crushed the irritating bug in his grasp, except there is no such evidence upon his empty palms and, between the open windows and his awful luck, those pesky thing would only come streaming _in_ , not out.

Abruptly, he feels something like a tickling on the top of his forehead.

His fist falls before he's barely aware himself of what he is doing, and finally, he gains a taste of one of his own punches.

It doesn't hurt as badly as it might otherwise have done, because obviously it was his _own_ punch and it would possibly have been a little strange if he couldn't withstand the force of his own fists, but he falls to the ground and rolls around on his futon for a little bit anyway, hissing and growling all manners of indecencies because: a) he'd missed the mosquito, b) it did hurt a little bit and c) it was far too embarrassing for a hero to have punched himself in the face and – oh, and now the lights are on and Genos is staring down at him with his mouth slightly open.

" _Sensei_!" The young cyborg exclaims, golden irises wide with alarm, and immediately Saitama feels metallic hands – warmed by the summer's heat – reaching down to assist him. " _Sensei_! A-Are you alright?"

Saitama decides that Genos doesn't need to know the truth and settles instead with an awkward smile. "Uh… I just hit my head on the table," he mutters, trying and failing to shake off the embarrassment. "I-It's nothing. Go back to sleep."

But the cyborg clearly isn't satisfied. He watches Saitama for a moment, his pupils oddly piercing, highlighted as they are against the dark sclera of mechanical eyes. " _Sensei,_ " he repeats, voice low but concerned. "I-If there's anything I can do to help… I heard you tossing and turning a while back, so I assume that you are perhaps struggling to sleep. If you need anything –"

"Hey dude, it's fine." Saitama rubs his face and sighs, wondering briefly why Genos can't behave like a normal teenager once in a while and just not care about anything. "Go back to sleep, don't worry about it."

"But _Sensei_ ," Genos protests, his circuits whirring and humming with barely suppressed anxiety, "I want to help. I'll do anything. I'm not a human anymore, I can afford to miss a few cycles of recharge."

 _So that's what he calls it_ , Saitama muses to himself, wondering on the odd phenomenon he has stumbled upon once or twice. To be honest, Genos doesn't look any different whether he is 'recharging' or 'online'. The only noticeable contrasts in which Saitama could identify between the two is a quieter hum in the teens' complex, mechanical biology and an odd, blinking yellow light which would wink on and off at his neck. Besides that, nothing, just the firm presence of a gratifyingly ' _Sensei_!'-less peace.

The Genos right now, however, is very much 'online' and without the slightest hint of, er, 'recharg-iness' in his visage. From his arms and chest there permeats a soft, orange glow, still visible despite the vest he has donned over it, and his eyes are far more earnest than a mechanical being such as himself really should have been capable of expressing.

Seeing Saitama's blank expression, the teen leans just that little bit closer until the distance between them is almost uncomfortable. " _Sensei_!"

At that moment, Saitama slaps himself.

The cyborg jerks back. Partly due to the shockwaves the impact has produced and partly from a mixture of surprise and horror. "S- _Sensei_!"

Saitama rubs his cheek. This time, he has been more careful in controlling his strength and the impact merely stings. "Damn, missed again." He curses, his eyes drifting about the room as though searching for an unseen enemy.

Riled by this thought, Genos tenses. "I-Is there a monster approaching?" He asks, voice low with apprehension, his radar already expanding outwards to scan the surrounding 10km for threat. It happens, sometimes, monsters appearing out of nowhere to attack the city, regardless of the time of day. _And if it's had Sensei up, worrying, in the middle of the night…_ Well, it most certainly would be a force to be reckoned with.

And yet no matter how carefully he grooms the surrounding area, there is nothing. The monster must be even further, he realises, eyes widening, far beyond the reach of his mere scanners. Somewhere deep within him, his Core hums. _As expected of Sensei! His innate ability to sense danger even from such a distance… I can't even begin to –_

"Ah, no, it's just a mosquito," Saitama explains, with a pained grimace as he detects the familiar whine once more. "It's been buzzing around all night and I can't –" Another clap of the hands. Nothing. "- Can't get to it. Ugh… It's such a…"

He drifts off when he becomes aware that his so-called 'disciple' is watching him with a dazed, awed expression and is evidently not listening at all. Sighing, he snaps his fingers and raises a sceptical brow when the young cyborg finally snaps back into reality.

" _Sensei_?"

"Hellooooo," Saitama tilts his head to one side. "Yes, that's me. I was just saying, there's a mosquito –"

"Ah," Genos nods in understanding, and allows a small, rare smile to cross his usual, taciturn features. "Yes. Now that I think about it, it was that bug which brought me to you, _Sensei_ , wasn't it?" He stares down at his metallic palms, voice soft with nostalgia. _Even though we just met a few months ago…_ "In some ways, you could say it was almost sent as a… as a guidance to me. Without that monster, I would never have been able to meet someone as… amazing as _Sensei_ …" His voice drops and he idly caresses one arm as though it may suddenly fall off. "I can't imagine what it would be like, at all, without _Sensei_ in my life…"

 _I can_ , thinks Saitama wistfully, basking in the memories of a happy, blissful life he had once been owner to prior to Genos' uncalled for intrusion, although admittedly now the washing up and laundry are getting done more frequently than they had been. Still, he worries sometimes, whether it really is the right thing for such an apparently promising S-Class Hero to sit in the same shoddy apartment as a mere C-Class and drink in his every word like motor oil.

"Um… Yeah," he says, awkwardly, after a while, because Genos has rambled on and he hasn't been listening. "Well… I'm happy for you, dude, but, uh, it's late, so I'm gonna try to sleep now, and –" _Bzzzz_. "Ugh! I missed again! Where'd it go…?"

"Is the bug troubling you, _Sensei_?" Genos perks up now, voice hopeful, and Saitama turns to find the teens' pupils flashing with numbers and coding as he scans the room with calculated calm. And then, before the bald hero could even utter a single syllable –

The temperature of the room rises sharply and a jet of flames erupt from Genos' palm, and when the blinding flash eventually dies, there is - for the first time in what felt to Saitama like a long time - blissful _silence_.

"Target eliminated," says Genos, simply, then turns to his master, hesitant once more. "Did that… help, _Sensei_?"

Saitama merely blinks. _Silence_.

"… Yeah." He says, eventually, and finds himself smiling. "Yeah. Thanks, Genos. You did a good job."

The cyborg stares for a long moment, as though uncomprehending of the words he has just heard, and then something delighted shines through his entire being until he is positively – and literally – glowing. "Really, _Sensei_?" He asks, almost choking, and there is something about his expression, something so strangely pure and _innocent_ , which makes him appear, in that instant, more like a child than any battle-hardened, S-Class Hero should appear.

And Saitama finds that he doesn't mind that at all. He smiles.

"Yeah," he nods. "That was great. That was something I'd never be able to do, alright." He flops back down on the futon. " _Ahhh_ , maybe I can finally sleep in peace, now."

Genos stares down at him from where he is kneeling on the floor. "If _Sensei_ wants me to," he offers, tentatively but with odd determination, "I can keep watch. I can detect any similar life forms in the vicinity, and I will eliminate them all, if it means _Sensei_ will be able to sleep better at night."

The offer hangs for a moment, apprehensive, in the air.

The virtuous side of Saitama knows immediately that the right thing to do would be to refuse. It would be abuse of the kid's desire to please, and he feels certain that his conscience would not settle knowing that Genos is only with him in the hope that Saitama would be offering _him_ something, and not the other way round. The cyborg, whether he likes it or not, is his student, not his slave. He couldn't... possibly use him like that.

And then the decidedly more unheroic side of Saitama argues that his body requires a good night's sleep _in order to_ be a better teacher to said cyborg. Not to mention the fact that it was Genos' offer in the first place, and as his teacher, he has no desire to, er, suppress his student's freedom. In fact, Genos would probably welcome the chance to keep himself occupied, since he apparently didn't 'recharge' anyway. Essentially, it was a win-win situation for the both of them.

… OK, so his reasoning is a little bit more twisted than it probably should have been, but Saitama thinks to himself that he will do something extra-nice to make up for the hard work afterwards, and mentions it too, aloud, so that Genos can remind him when he inevitably forgets.

But the teen merely shakes his head.

"Having _Sensei_ accept me as his disciple is more than enough," he states, keenly. "I owe you too much, _Sensei_. If it would help, I am willing to chase away mosquitoes for you every night."

… Saitama has to admit that he is more than a little tempted.

"OK," he acquits, rolling to switch off the lights before laying himself back upon the futon. Genos' glowing orbs follow his every movement and, in the darkness, his pupils appear almost to be floating. "I'll take that offer." He pauses for a moment, attempting to look for some justification in his actions. "Tell you what," he says, after a while, "think of this as training."

The teen's head snaps up at the words. Saitama can hear the machinery in his neck creak with the sudden movement. "Training?"

"Yeah," Saitama nods, with confidence, though he knows he's bluffing and doesn't quite know why he sounds so sure of himself. "You have to, um, eliminate those mosquitoes without waking me up, or destroying any of the buildings, or apartment, or furniture, or, er, anything." That sounded like a… plausible enough test... Right? "It would be a good way to demonstrate your abilities." He tacks on, as an afterthought, as though that would somehow make the whole thing sound much less lame.

"I see!" says Genos, wide-eyed, and Saitama is a little bemused that he can actually see anything. (Well, aside from the fact that Genos _could_ see in the dark, being a cyborg and all with fancy, infra-red lenses for eyes, but, still, it was almost impressive to see the extent to which the kid could misinterpret his words.) "So _Sensei_ has noticed that I have difficulty in controlling my strength…" His fingers tap thoughtfully upon synthetic skin, emitting an oddly rhythmical ' _clunk_ ' sound. "Indeed, put to practical use on the battlefield, it would be troublesome to waste energy on weaker foes when power should be conserved for the potentially more dangerous monsters. Hmm… I see." He looks up now, golden orbs glittering with conviction. "Then I shall do my best to eliminate all the mosquitoes in the area without waking _Sensei_ and without destroying any buildings, the apartment, the furniture, or anything."

"… Yeah," says Saitama lamely, because it's far too early in the morning to listen to anything that is more than ten words long, so he simply doesn't comment - lest he inspires another speech - and settles for throwing his blankets over his chin. "Oh, by the way, you have fans installed in you too, right? 'Cos it'd be good if you could lower the temperature a bit. Summers should be illegal."

Instantly, there is a whirring besides his futon and Saitama sighs contentedly as the rush of the cool air hits his face. Even behind his eyelids he could sense the golden glow of Genos' eyes watching over him faithfully.

"See, this is where you're stronger than me," the bald hero mumbles gratefully, stifling a yawn as he scratches his hairless head and allows his body to relax. "You can catch mosquitoes when I can't, be a natural air con when I can't… I wish I could be a bit more like you, you know?"

And if he were to be perfectly honest, he did intend it to be some sort of light-hearted joke, but suddenly besides him there is the sound of abruptly locking gears and a short crackle of electricity where something deep within the cyborg has short-circuited.

 _Seriously…? He took that as a compliment?_

Saitama throws his blanket over his face and sighs.

Then he remembers the way Genos' face has once lit up at his words and, for an odd reason, finds himself hoping – just a little bit, because he's a caring _sensei_ after all – that the same smile is illuminating the darkness now.

And sleep comes to him a lot easier after that, accompanied by the soft whirring of fans, the occasional bursts of flames, and the gentle silence guarded diligently by his young, metallic disciple.

* * *

 **A/N:** Thank you for reading! Please drop me a review and tell me what you think. Any words of advice would be appreciated too, because, as you can see, I'm entirely new to this series but loving it already. ^_^ Thanks again!


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